An implantable medical device, for the delivery of stimulation therapy, may include an electrode and a fixation component configured to hold the electrode in intimate contact with tissue at a stimulation site. One type of such a device may be an implantable cardiac pacemaker that includes a pulse generator and a pacing electrode coupled to the generator, for example, by an elongate insulated lead wire. A pacing site may be located on an epicardial surface of the heart, for example, on the left side of the heart for the application of pacing therapy to treat heart failure. FIG. 1 is a schematic showing an access site A for creating a passageway between a patient's diaphragm 19 and xiphoid process 20 of sternum 13, for example, to implant a pacing electrode on an epicardial surface 6 of the patient's heart, which is enclosed within the pericardial sac 15. After making a superficial incision, an operator may open a passageway between diaphragmatic attachments 18 and diaphragm 19 by using blunt dissection tools and techniques that are known in the art. Then, the operator may employ a piercing tool to pass a guide wire through the pericardial sac 15, also according to methods known in the art. The operator may use fluoroscopic guidance to position a distal portion of the guide wire along a portion of epicardial surface 6, at which a target site is located, and then pass a guiding sheath over the positioned guide wire. The guiding sheath then serves as a conduit for delivery of the implantable electrode to the target site. In this context, to deliver and then fix, or secure the implantable electrode at an epicardial site, there is a need for new configurations of interventional systems and associated implantable device assemblies.